One type of memory storage device is a magnetic random access memory (MRAM). MRAM is a type of non-volatile magnetic memory which includes magnetic memory cells. A typical magnetic memory cell includes a layer of magnetic film in which the magnetization of the magnetic film is alterable and a layer of magnetic film in which magnetization is fixed or “pinned” in a particular direction. The magnetic film having alterable magnetization is typically referred to as a data storage layer, and the magnetic film which is pinned is typically referred to as a reference layer.
A typical magnetic memory includes an array of magnetic memory cells. Word lines extend along rows of the magnetic memory cells, and bit lines extend along columns of the magnetic memory cells. Each magnetic memory cell is located at an intersection of a word line and a bit line. A magnetic memory cell is usually written to a desired logic state by applying external magnetic fields that rotate the orientation of magnetization in its data storage layer. The logic state of a magnetic memory cell is indicated by its resistance state which depends on the relative orientations of magnetization in its data storage and reference layers. A sense amplifier is used to sense the resistance state of a selected magnetic memory cell to determine the logic state stored in the memory cell.
Traditionally, memory arrays have been designed for applications which require high data transfer rates or low power consumption. For applications requiring high data transfer rates, parallel designs which increase the number of input/output ports can be used or the operating speed of the memory arrays can be increased. With either of these approaches, the higher data transfer rates result in increased power consumption. Once the physical design of the memory is optimized for a particular application, such as one requiring high data transfer rates, the memory may not be suitable for other applications.
Recently, low-cost and portable devices such as personal digital assistants (PDAs) have been made possible by improvements in technology which have reduced their weight and capacity to store information. The PDAs can be used to store frequently used information such as daily appointments, task lists, and telephone contact information. This information is typically retrieved in small amounts as needed from the PDA in situations where power for the PDA is supplied by batteries.
The PDAs are able to exchange information with personal computers for the purpose of backup data storage. The backup data storage activity transfers a significant amount of information to the personal computer so high data transfer rates are desirable. The backup data storage is usually performed in an environment such as at a home or office where power receptacles are readily available to supply power to the PDA.